Intervertebral prosthesis or nucleus replacement prosthesis

ABSTRACT

An intervertebral disk prosthesis or nuclear prosthesis ( 1 ) includes a longitudinal, flexibility-yielding object ( 2 ) that can be spiral-wound ( 2 ), with a first exterior end ( 3 ), a second interior end ( 4 ) and a longitudinal central axis ( 5 ). The cross-section ( 10 ) of the object ( 2 ), which is orthogonal towards the central axis ( 5 ), is reduced in size towards the second interior end ( 4 ).

The invention relates to an intervertebal prosthesis or nuclearprosthesis as per to the generic term of patent claim 1.

Such prostheses are inserted into the intervertebral disk space betweentwo adjacent vertebral bodies, after removal of the damaged natural diskor the damaged nucleus of a disk. The intended objective is to recreateconditions resembling the natural conditions as closely as possible,which means in particular restoring the height of the original disk andthereby restoring the original spacing between two adjacent vertebralbodies.

From the state of the art intervertebral disk prostheses are alreadyknown, for example from FR-A-2 712 486 BRESLAVE, whereby a bendable butnot flexibility-yielding VELKRO tape is spiral-wound to form a circulardisk. To enable winding the tape in a spiral shape, this knownprosthesis requires a cylindrical centre piece to which the tape isattached and then wound around it by rotating the centre-piece.

A disadvantage of this known intervertebral disk prosthesis is thetransition between the relatively large centre piece and the relativelynarrow tape as well as the lacking elasticity-yield of the tape. Thesize of the centre piece at the same time also determines the size ofthe entry opening, whereby the latter should be kept as small aspossible which, however, is impossible with this known prosthesis.

From EP-A-0 773 008 an intervertebral prosthesis according to thegeneric term under claim 1 is known. A disadvantage of this knownprosthesis is again the relatively large cylindrical centre piece towhich the elongated, spiral-shaped object is attached with a linkingcomponent of a lesser width which acts as a joint. Handling of thecylindrical centre piece with the successive articulate linkingcomponent is difficult and requires effort—precisely because it isshaped to be springy and articulate. Furthermore, the cylindrical centrepiece is obtrusive.

The above discussion of the state of the art was merely entered into todescribe the context of the invention and does not mean that at the timeof this application or its priority, the state of the art had actuallybeen publicised or was public knowledge.

The invention intends to resolve these issues. The invention is based onthe challenge of producing an intervertebral disk prosthesis or nucleusprosthesis which due to its geometric shape restores the height of theintervertebral disk, absorbs any occurring acting forces across theentire—preferably convex-shaped —surface and reduces the pressure in thefacet joints, diverts forces to the anulus while not aversely affectingthe natural movement but supporting it.

The reduced size of the interior end of the intervertebral diskprosthesis or nuclear prosthesis enables easier handling of theinstruments. As a result the resistance when drawing the implant intothe inserting instrument lessens.

The endplate centre is very thin and can therefore be pushed inrelatively easily; on account of the thinner cross section in the centreof the implant, it is designed as a relatively flexible zone, so thatthe occurring pressures are better absorbed.

The invention solves the task at hand with an intervertebral diskprosthesis featuring the characteristics of claim 1.

The reduction of the cross section which is orthogonal to the centralaxis, preferably occurs continuously and preferably towards the firstexterior end of the object. The width of the object, measured verticallyto the central axis, should also be reduced—preferablycontinuously—beginning from its centre towards the exterior end. Inaddition, the width may also be reduced towards the interior end,preferably continuously. In this manner an increased flexibility of theinstruments for handling the implant is achieved.

In its centre the width of the object is typically wider by 50% to 500%,preferably by 100% to 300% compared with its interior and exterior end.Thereby individual flexibility can be controlled and a larger bearingsurface towards the cover plates of the vertebral bodies is achieved.

In a specific embodiment of the invention with the object in aspiral-wound state to the central axis, it features an upper spirallevel and a lower spiral level, both of which arched in a convex-shapeand suitable for application to the cover plates of two adjointvertebral bodies. This achieves self-centering of the implant within theconcave endplates of the vertebral bodies and a height increase of theapplication surface as well as a reduction of the specific surfacepressures. Overall this results in a better transfer of forces to theanulus and the endplate.

Suitably, in its spiral-wound and unloaded state, the object has a gapwhich on the one hand facilitates the production of the object and onthe other hand guarantees optimum flexibility. The gap should have awidth of a minimum of 0.4 mm, preferably a minimum of 0.5 mm. On theother hand the gap should not exceed a maximum width of 1.0 mm, with thepreferred maximum being 0.8 mm. Within these ranges an optimum memoryeffect of the object with spiral winding occurs.

In a specific embodiment of the invention, the object in itsspiral-wound state—viewed from the spiral level—features an oval orkidney-shaped shape, preferably with a surface between 250 to 750 mm²measured at the spiral level, which results in an optimum adjustment tothe anatomical contributing conditions.

In a preferred embodiment of the invention the object contains ahydrogel or is even exclusively made up of hydrogel. Hydrogels arecolloids in which the dispersal phase (colloid) has combined with thecontinuous phase (water) to form a viscous, gel-like compound, e.g.coagulated silicon acid. Compared with other materials this brings thebenefit of releasing water when under pressure and absorbing water withload relief, which means it acts analogous to the natural nucleus.

Suitably, the object is manufactured using an injection-molding processwhereby its injection point is preferably located in the area of thesecond end. For the production this is an advantage in terms of thefilling process. Preferably the injection point is placed in a recessedposition. Therefore, warping caused by pulling out the needle nozzle,does not occur on the surface but inside the recess.

In a specific embodiment of the invention the first end is designedasymmetrically towards the interior of the spiral. This results in theexterior form of the object with spiral winding to be rounded.

The object can be designed to be X-ray-opaque, preferably by using theadditive barium sulfate. This allows checking the current position ofthe implant and monitoring any possible migration. For the same purposethe object may also contain X-ray-opaque components, preferably in theform of filaments, wires or tiny globes.

In a specific embodiment of the invention the last exterior turn of thespiral, amounting to at least 360° C. of the circumference of thespiral-wound object, has a thinner cross section when compared with theremaining spiral turns. As a result the exterior rim of the implant ismore flexible in terms of the function of the implant.

Finally, the exterior end of the object can be fitted with aids suitablefor gripping the intervertebral disk prosthesis using an insertinginstrument, preferably in the form of indentations or protrusions.

The following describes the invention and extensions of the invention inmore detail by means of schematic illustrations of an embodiment of theinvention.

It shows

FIG. 1—a view shown in perspective of an intervertebral disk prosthesisin terms of the invention;

FIG. 2 shows a horizontal cross section through the intervertebral diskprosthesis as per FIG. 1;

FIG. 3 shows a cross section along the line III-III in FIG. 2;

FIG. 4—a side view of the intervertebral disk prosthesis as per FIG. 1;

FIG. 5—an enlarged section of FIG. 3 in the area of the centralinjection point;

FIG. 6—an enlarged view shown in perspective of the exterior end of theobject with spiral winding as per FIG. 1; and

FIG. 7 a variant of the exterior end of the object with spiral windingas per FIG. 1.

The intervertebral disk prosthesis 1 shown in FIG. 1 to 4 consists of alongitudinal, flexibility-yielding object 2 which may be spiral-woundwith a first exterior end 3 and a second interior end 4 and alongitudinal central axis 5. The cross section 10 which is orthogonal tothe centre axis 5 of the object 2, is reduced continuously—as shown inFIGS. 2 and 3—towards the second interior end 4 as well as towards thefirst exterior end 3.

The measured width of object 2 in FIG. 2 at its interior end 4 amountsto circa 2.5 mm, at the exterior end 3 it is also circa 2.5 mm and inbetween towards the centre of the object it increases to up to circa 4.5mm.

The measured height of the intervertebral prosthesis 1 measured in FIG.3 corresponds to the anatomical intervertebral disk space. In the centreof the convex intervertebral disk prosthesis 1, the height on both sidesprotrudes by circa 0.5 to 3.0 in comparison to the sections located onthe rim.

In a spiral-wound, unloaded state of object 2—as shown in FIGS. 1 and 2—there is a gap of 0.65 mm between each individual spiral turn.

Essentially object 2 consists of an envelope of polycarbonate urethaneand/or silicon polycarbonate urethane as well as of a filling ofpolyvinyl alcohol hydrogel. Further suitable materials both for theenvelope as well as for its filling may be obtained from the pendingInternational Patent Application PCT/CHO1/00700.

FIG. 5 shows how injection point 9 is located in the area of the secondend, which means nearly in the centre of the spiral-shaped object 2 andhow it is recessed when compared with the upper spiral level 6.

FIG. 6 shows a possible variant of the exterior end 3 of object 2 withaids in the form of two grooves 11 located crossways to the central axis5, which allow gripping the intervertebral disk prosthesis using asuitable insertion instrument, for example tongs.

FIG. 7 shows a second variant of the exterior end 3 of object 2 withaids, in this case in form of two shallow indentations 12 runningcrossways towards the central axis 5 as well as a slit 13 with acylindrical counterdraft 14 positioned parallel to the central axis.

1. An intervertebral disk prosthesis or nuclear prosthesis (1)consisting of a longitudinal, flexibility-yielding object that isadapted to be wound in a spiral shape (2), with a first exterior end(3), a second interior end (4) and a longitudinal central axis (5),wherein a cross-section (10) of the object (2) which is orthogonaltowards the central axis (5) is reduced in size towards the secondinterior end (4).
 2. The intervertebral disk prosthesis (1) according toclaim 1, wherein the orthogonal cross-section (10) is continuouslyreduced in size.
 3. The intervertebral disk prosthesis (1) according toclaim 1, wherein the cross-section (10) of the object (2), which isorthogonal towards the central axis (5), is continuously reduced in sizetowards the first exterior end (3), preferably with the reductionoccurring continuously.
 4. The intervertebral disk prosthesis (1)according to claim 1, wherein a measured width of the object (2),running vertically towards the central axis (5), is reduced in size,when viewed from its center toward the exterior end (3), and wherein themeasured width reduction occurs continuously.
 5. The intervertebral diskprosthesis (1) according to claim 1, wherein a measured width of theobject (2), running vertically towards the central axis (5), is reducedin size when viewed from its center toward the inner end (4), andwherein the measured width reduction occurs continuously.
 6. Theintervertebral disk prosthesis (1) according to claim 1, wherein a widthof the object (2) in its center is wider by 50% to 500%, preferablywider by 100% to 300%, than at its interior and exterior ends (4, 3). 7.The intervertebral disk prosthesis (1) according to claim 1, wherein theobject (2) in its spiral-wound state towards the central axis (5)features an upper spiral level (6) and a lower spiral level (7), whichare both curved in convex shapes and are suitable for application tocover plates of two adjacent intervertebral disk spaces.
 8. Theintervertebral disk prosthesis (1) according to claim 1, wherein theobject (2) in a spiral-wound unloaded state features a gap between thespirals.
 9. The intervertebral disk prosthesis (1) according to claim 8,wherein the gap has a minimum width of 0.4 mm.
 10. The intervertebraldisk prosthesis (1) according to claim 8, wherien the gap has a maximumwidth of 1 mm.
 11. The intervertebral disk prosthesis (1) according toclaim 1, wherein the object (2) in a spiral-wound state, when viewed atthe spiral level, features an oval or kidney-shaped shape, and having asurface between 250 to 750 mm² measured at the spiral level.
 12. Theintervertebral disk prosthesis (1) according to claim 1, wherein theobject (2) contains a hydrogel.
 13. The intervertebral disk prosthesis(1) according to claim 1, wherein the object (2) is manufactured usingan injection-molding process and its injection point (9) is positionedin an area of the second end (4).
 14. The intervertebral disk prosthesis(1) according to claim 13, wherein the injection point (9) is located ina recess vis-à-vis the upper spiral level (6).
 15. The intervertebraldisk prosthesis (1) according to claim 1, wherein the first end (3) isdesigned asymmetrically towards an interior of the spiral.
 16. Theintervertebral disk prosthesis (1) according to claim 1, wherein theobject (2) is X-ray-opaque.
 17. The intervertebral disk prosthesis (1)according to claim 1, wherein the object (2) contains X-ray-opaquecomponents.
 18. The intervertebral disk prosthesis (1) according toclaim 1, wherein a last exterior spiral turn with a circumference of atleast 3600 of the spiral-wound object (2) has a thinner cross-sectionthan remaining spiral turns.
 19. The intervertebral disk prosthesis (1)according to claim 1 wherein the exterior end (3) of the object (2) isfitted with aids (11, 12, 13, 14), which are suited for gripping theintervertebral disk prosthesis (1) using an insertion instrument.